1. Field of the Invention
The present invention relates to a delivery apparatus for pressurized medical liquids and in particular to a re-fillable delivery apparatus for pressurized liquid anaesthetics.
2. Description of the Prior Art
It is known to provide a delivery apparatus for pressurized liquid anaesthetic which has a primary reservoir having an inlet for refilling with the liquid anaesthetic, a primary pressurizing arrangement, typically a source of pressurized inert gas and a pressure regulator, for maintaining liquid within the primary reservoir at a delivery pressure, and an outlet through which the pressurized liquid anaesthetic is controllably delivered at the delivery pressure. Normally, to refill the primary reservoir of this known apparatus either the delivery pressure must be removed and fresh liquid introduced through the inlet at atmospheric pressure, or liquid anaesthetic at the delivery pressure must be introduced through the inlet. The former has the disadvantage that the delivery of the pressurized liquid anaesthetic must be stopped during refilling and the latter has the disadvantages that pressurized liquid anaesthetic may escape into the local environment or that the delivery apparatus may become over-pressurized, which may cause either escape of anaesthetic into the local environment or an error in the delivered amount of the liquid anaesthetic.